Conventional coolant pumps, also referred to as water pumps, are typically mounted on the front of the engine frame so that the pump can be operated by a belt drive system. Specifically, the output shaft, or crankshaft, of the engine includes a driving pulley fixed thereto forming part of the drive system. The drive system includes an endless belt that is trained about the driving pulley and a sequence of driven pulley assemblies, each of which is fixed to a respective shaft. The shafts are connected to operate various engine or vehicle accessories. For example, one shaft may drive the water pump, and the other shafts may drive such accessories as an electrical alternator, an electromagnetic clutch of a compressor for an air-conditioning system, or an oil pump of the power steering system. With the abundance of accessories, there is limited space in the front of the engine.
To address this issue, it is known to mount the water pump on the back of the engine and operatively connect the pump shaft to the back end of the camshaft in order to drive the pump shaft. An example of this type of water pump is disclosed in U.S. Pat. No. 4,917,052 to Eguchi et al.
However, the camshaft is subjected to torsional vibrations due to, for example, the natural operating frequency of the engine, cyclic resistance to camshaft rotation, and vibrations occurring in the camshaft drive chain/belt. Such torsional vibrations can cause excessive wear in the chain/belt and at the cam surfaces. As a result, it is known to provide vibration damping means for the camshaft so torsional vibrations may be damped. An example of a camshaft damper is disclosed in U.S. Pat. No. 4,848,183 to Ferguson.
Thus, there is a need for a water pump that can be operated by the camshaft of the internal combustion engine and can also act as a torsional vibration damper for the camshaft. Additionally, there is always a need in the automotive art to provide more cost-effective components. The present invention addresses these needs in the art as well as other needs, which will become apparent to those skilled in the art once given this disclosure.
GP Patent No. 1,567,303 discloses a water pump impeller connected to the end of a camshaft. Camshaft driven water pumps, such as those disclosed in the '052 U.S. patent and the '303 GB patent, have not been commercially viable. The applicant has determined that part of the problem associated with camshaft driven water pumps is that they place heavy loads on the camshaft as a result of the pumping action. Unlike water pumps that have bearings that are adapted to accommodate both radial and axial loads, camshafts have bearings that primarily accommodate radial loads. While camshaft bearings may accommodate minute axial loads that occur during normal operating conditions, the camshaft is not configured to accommodate substantial axial loads as would be generated by a water pump impeller.
Thus, another aspect of the present invention relates to a water pump that is operated by the camshaft of the internal combustion engine and that is structured to substantially reduce or eliminate the transfer of axial loads from the water pump impeller to the camshaft.